Tuberculosis is an infectious disease most commonly associated with the lungs, but which can affect almost any tissue or organ in the body. Its primary cause is an acid-fast bacillus, Mycobacterium tuberculosis. It is usually a chronic disease that lingers for months and sometimes years, but acute forms, which most commonly strike infants and young children, can prove fatal in a matter of weeks or days. One acute form is called miliary tuberculosis because of the small, grainlike tubercles it creates simultaneously in almost every organ of the body. From ancient times, tuberculosis was endemic in most populations of Eurasia, North Africa, and possibly the Americas, affecting relatively small numbers of people and maintaining low prevalence rates. But with the rise of urban and industrial development between the eighteenth and twentieth centuries, it became epidemic in much of Europe, North and South America, and Africa and Asia. In some places during this time most people were exposed to this disease, and its prevalence rates approached 100 percent of the population. Tuberculosis killed millions of people, placing it, despite its chronicity, on a historical par with the great global epidemic diseases of bubonic plague, cholera, measles, smallpox, typhoid, typhus, and the like. Until 1944, there was no specific drug therapy for it. In that year, researchers discovered streptomycin, which proved effective in inhibiting the disease. Two more drugs, para-aminosalicylic acid (PAS) and isoniazid (isonicotinic acid hydrazide, or INH), discovered in 1946 and 1952, respectively, provided an extremely effective treatment when used in combination with streptomycin.